Because of advancements in emergency cardiac care and the proliferation of pre-hospital advanced life support services, it is now possible for out-of-hospital heart attack victims to survive attacks which would have resulted in certain death in the past. However, the efficacy of any such emergency care decreases dramatically as the time interval from the onset of the heart attack to the beginning of treatment increases. Rapid care is most urgently required in cases of cardiac arrest, where treatment must begin almost immediately after the attack if the victim is to be resuscitated. Yet, in all cardiac arrests and in many other types of serious heart attacks, the victim is incapacitated and cannot summon assistance. Therefore, if a serious heart attack is not witnessed, help will probably not arrive promptly and the victim will probably not survive.
Since almost all heart attacks occur outside of the hospital and since out-of-hospital cardiac arrests account for most of the heart attack deaths, the inventors have noted that persons significantly at risk of suffering a heart attack, such as persons with a history of heart trouble and the elderly, could benefit from a system designed for continuous everyday use outside of the hospital which automatically summons aid in case of a cardiac arrest and which provides its users with a way to manually signal for aid in other types of cardiac and non-cardiac emergencies. Preferably, such a system would perform these functions without restricting freedom of movement or interfering with the user's daily routine.
Hospital cardiac care units now routinely attach heart monitors to their patients These hospital monitoring systems can immediately summon aid in case of a cardiac emergency, but they are not designed for comfort and are thus inappropriate for everyday use outside of the hospital A typical monitoring system consists of a box-like monitoring device which obtains heart function data from electrodes that are attached to a patient's chest by adhesive patches and are connected to the monitoring device by wires. The monitoring device transmits the heart function information to a central station, either through more wires or by radio frequency (RF) signals. One such system is described in U.S. Pat. No. 3,902,478 to Konopasek et al. Other systems, such as the one described in U.S. Pat. No. 4,827,943 to Bornn et al. require that the patient wear a bulky vest-like device. However, along with being burdensome for any normally active person who is not in the hospital, such monitoring systems are often troubled by false alarms.
A number of systems have been proposed which fit on a person's wrist and determine heart functions by checking the wearer's pulse. These systems typically have transmitters which signal an alarm in the event of a cardiac emergency. Such systems are shown in U.S. Pat. Nos. 3,927,320 to Kalman, No. 4,819,860 to Hargrove et al., and No. 3,572,316 to Vogleman et al. Such systems use various types of sensors which are attached to the wrist to calculate pulse rates, including pressure sensors (U.S. Pat. No. 4,406,290), sonic sensors (U.S. Pat. No. 4,489,731), and electrode-type sensors (U.S. Pat. No. 4,120,294). A relatively new method of detecting a person's pulse by using infrared light is disclosed by Cramer et al. in U.S. Pat. No. 4,224,948 and is also referred to in U.S. Pat. No. 4,819,860. In this method, infrared light is beamed onto the palm side of the wrist and the change in the intensity of light that is reflected into a detector is used to calculate a person's blood flow and thus his pulse rate. Yet, while these wrist-based systems are less burdensome than some other types of cardiac monitors, no system known to the inventors has the desired attributes and is further primarily designed for use in the home, where almost all heart attacks occur.
Some less-sophisticated in-home monitoring devices have been proposed For example, U.S. Pat. No. 4,829,285 to Brand et al. and U.S. Pat. No. 3,866,204 to Barkley disclose systems having a portable device with a tilt switch. If the user collapses, an alarm signal is sent to a fixed station. Yet, such systems can produce many false alarms or fail to cause an alarm when a heart attack occurs since they do not actually monitor heart function. Other in-home systems are comprised of a portable unit, which is often worn around the neck, and a stationary unit. If the person wearing the portable unit presses its button, the portable unit will send an RF signal to the stationary unit. This RF signal drives the stationary unit to call a central station, and the operator who answers the telephone call tries to communicate with the user of the system through a speakerphone to determine if assistance should be sent to the user's home. Components of such systems are shown generally in U.S. Pat. Nos. 3,989,900, 4,064,368, and 4,491,970. Although such systems are advertised as helpful for heart attacks, they are completely ineffective in bringing cardiac arrest victims faster help because these victims are unable to press the button to signal for help before they become unconscious.
In addressing all of the shortcomings of the previously proposed systems, the inventors have determined that the ideal out-of-hospital monitoring and warning system would include an accurate and unobtrusive pulse monitor, a miniaturized, fail-safe transmitter capable of transmitting automatically and manually-generated emergency signals, and a device for receiving the emergency signals and automatically alerting the appropriate rescue parties. However, so far as the inventors are aware, none of the known systems provide all these functions in a convenient, reliable, and affordable manner. Specifically, none of the systems described above combine obstrusive, energy-efficient, and false-alarm proof wrist-mounted pulse detection systems with miniaturized fail-safe emergency signal transmitters and dedicated base units that monitor the transmissions and summon help automatically when necessary even if the victim is outside of the hospital.